Hawking Radiation from Acoustic Black Holes, Short Distance and Back-Reaction Effects

Using the action principle we first review how linear density perturbations (sound waves) in an Eulerian fluid obey a relativistic equation: the d'Alembert equation. This analogy between propagation of sound and that of a massless scalar field in a Lorentzian metric also applies to non-homogeneous flows. In these cases, sound waves effectively propagate in a curved four-dimensional ''acoustic'' metric whose properties are determined by the flow. Using this analogy, we consider regular flows which become supersonic, and show that the acoustic metric behaves like that of a black hole. The analogy is so good that, when considering quantum mechanics, acoustic black holes should produce a thermal flux of Hawking phonons. We then focus on two interesting questions related to Hawking radiation which are not fully understood in the context of gravitational black holes due to the lack of a theory of quantum gravity. The first concerns the calculation of the modifications of Hawking radiation which are induced by dispersive effects at short distances, i.e., approaching the atomic scale when considering sound. We generalize existing treatments and calculate the modifications caused by the propagation near the black hole horizon. The second question concerns backreaction effects. We return to the Eulerian action, compute second order effects, and show that the backreaction of sound waves on the fluid's flow can be expressed in terms of their stress-energy tensor. Using this result in the context of Hawking radiation, we compute the secular effect on the background flow.Comment: 60 pages, 6 figures. Review submitted to "La Rivista del Nuovo Cimento

Quantum effects in Acoustic Black Holes: the Backreaction

We investigate the backreaction equations for an acoustic black hole formed in a Laval nozzle under the assumption that the motion of the fluid is one-dimensional. The solution in the near-horizon region shows that as phonons are (thermally) radiated the sonic horizon shrinks and the temperature decreases. This contrasts with the behaviour of Schwarzschild black holes, and is similar to what happens in the evaporation of (near-extremal) Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by appropriate boundary conditions the solution is extended in both the asymptotic regions of the nozzle.Comment: 23 pages, latex, 1 figure; revised version, to appear in Phys. Rev.

Analogue Cosmological Particle Creation: Quantum Correlations in Expanding Bose Einstein Condensates

We investigate the structure of quantum correlations in an expanding Bose Einstein Condensate (BEC) through the analogue gravity framework. We consider both a 3+1 isotropically expanding BEC as well as the experimentally relevant case of an elongated, effectively 1+1 dimensional, expanding condensate. In this case we include the effects of inhomogeneities in the condensate, a feature rarely included in the analogue gravity literature. In both cases we link the BEC expansion to a simple model for an expanding spacetime and then study the correlation structure numerically and analytically (in suitable approximations). We also discuss the expected strength of such correlation patterns and experimentally feasible BEC systems in which these effects might be detected in the near future.Comment: Reference adde

Hawking Radiation from an Acoustic Black Hole on an Ion Ring

In this article we propose to simulate acoustic black holes with ions in rings. If the ions are rotating with a stationary and inhomogeneous velocity profile, regions can appear where the ion velocity exceeds the group velocity of the phonons. In these regions phonons are trapped like light in black holes, even though we have a discrete field theory and a nonlinear dispersion relation. We study the appearance of Hawking radiation in this setup and propose a scheme to detect it.Comment: 4 pages, 3 figures, minor revisions, published versio

Acoustic geometry for general relativistic barotropic irrotational fluid flow

"Acoustic spacetimes", in which techniques of differential geometry are used to investigate sound propagation in moving fluids, have attracted considerable attention over the last few decades. Most of the models currently considered in the literature are based on non-relativistic barotropic irrotational fluids, defined in a flat Newtonian background. The extension, first to special relativistic barotropic fluid flow, and then to general relativistic barotropic fluid flow in an arbitrary background, is less straightforward than it might at first appear. In this article we provide a pedagogical and simple derivation of the general relativistic "acoustic spacetime" in an arbitrary (d+1) dimensional curved-space background.Comment: V1: 23 pages, zero figures; V2: now 24 pages, some clarifications, 2 references added. This version accepted for publication in the New Journal of Physics. (Special issue on "Classical and Quantum Analogues for Gravitational Phenomena and Related Effects"

po 298 myc favours the onset of tumour initiating cells by inducing epigenetic reprogramming of mammary epithelial cells towards a stem cell like state

Introduction Breast cancer consists of highly heterogenous tumours whose cell of origin resulted difficult to be defined. Recent findings highlighted the possibility that tumor-initiating cells (TICs) may arise from dedifferentiation of lineage-committed cells, by reactivation of multipotency in response to oncogenic insults. MYC is the most frequently amplified oncogene in breast cancer and the activation of MYC pathway has been associated with the basal-like subtype, which is characterised by poor survival and lack of a specific therapeutic strategy. Although MYC has been considered a driver oncogene in breast cancer, its mechanism of action in tumour initiation has been poorly addressed. Material and methods To evaluate the role of MYC in perturbing cell identity of somatic cells, we transduced hTERT-immortalised human mammary epithelial cells (IMEC) with a retroviral vector expressing low levels of the exogenous c-Myc. The effect of MYC overexpression was evaluated by performing morphological analysis and gene expression profiling. To verify whether MYC overexpression could enrich for cells with functional stem cell-like properties, we performed mammospheres assay. ChIP-seq analyses were performed to profile chromatin modifications and MYC binding in IMEC WT, -MYC and mammospheres. To determine whether MYC-reprogrammed IMEC were enriched for TICs, we performed in vivo injection in NOD/SCID mice and assessed long-term tumorigenic potential by performing serial transplantation assay. To assess the clinical relevance of our findings, we investigated the expression of MYC-dependent oncogenic signature in a database of breast cancer patients. Results and discussions Overexpression of MYC induces transcriptional repression of lineage-specifying transcription factors, causing decommissioning of luminal-specific enhancers. Of note, MYC-driven dedifferentiation supports the onset of a basal/stem cell-like state by inducing the activation of de novo enhancers, which drive the transcriptional activation of oncogenic pathways. MYC-driven epigenetic reprogramming favours the formation and maintenance of TICs endowed with metastatic capacity. Moreover, oncogenic pathways activated by MYC-modulated enhancers are associated with basal-like breast cancer in patients with a poor prognosis. Conclusion MYC-driven tumour initiation relies on a cell reprogramming process, which is mediated by activation of MYC-dependent oncogenic enhancers, thus establishing a therapeutic rational for treating basal-like breast cancers

Some general properties of the renormalized stress-energy tensor for static quantum states on (n+1)-dimensional spherically symmetric black holes

We study the renormalized stress-energy tensor (RSET) for static quantum states on (n+1)-dimensional, static, spherically symmetric black holes. By solving the conservation equations, we are able to write the stress-energy tensor in terms of a single unknown function of the radial co-ordinate, plus two arbitrary constants. Conditions for the stress-energy tensor to be regular at event horizons (including the extremal and ``ultra-extremal'' cases) are then derived using generalized Kruskal-like co-ordinates. These results should be useful for future calculations of the RSET for static quantum states on spherically symmetric black hole geometries in any number of space-time dimensions.Comment: 9 pages, no figures, RevTeX4, references added, accepted for publication in General Relativity and Gravitatio

Relativistic quantum clocks

The conflict between quantum theory and the theory of relativity is exemplified in their treatment of time. We examine the ways in which their conceptions differ, and describe a semiclassical clock model combining elements of both theories. The results obtained with this clock model in flat spacetime are reviewed, and the problem of generalizing the model to curved spacetime is discussed, before briefly describing an experimental setup which could be used to test of the model. Taking an operationalist view, where time is that which is measured by a clock, we discuss the conclusions that can be drawn from these results, and what clues they contain for a full quantum relativistic theory of time.Comment: 12 pages, 4 figures. Invited contribution for the proceedings for "Workshop on Time in Physics" Zurich 201

Condensed matter lessons about the origin of time

It is widely hoped that quantum gravity will shed light on the question of the origin of time in physics. The currently dominant approaches to a candidate quantum theory of gravity have naturally evolved from general relativity, on the one hand, and from particle physics, on the other hand. A third important branch of 20th century `fundamental' physics, condensed-matter physics, also offers an interesting perspective on quantum gravity, and thereby on the problem of time. The bottomline might sound disappointing: to understand the origin of time, much more experimental input is needed than what is available today. Moreover it is far from obvious that we will ever find out the true origin of physical time, even if we become able to directly probe physics at the Planck scale. But we might learn some interesting lessons about time and the structure of our universe in the process. A first lesson is that there are probably several characteristic scales associated with "quantum gravity" effects, rather than the single Planck scale usually considered. These can differ by several orders of magnitude, and thereby conspire to hide certain effects expected from quantum gravity, rendering them undetectable even with Planck-scale experiments. A more tentative conclusion is that the hierarchy between general relativity, special relativity and Newtonian physics, usually taken for granted, might have to be interpreted with caution.Comment: v1: 9 pages. Fourth juried prize in FQXi essay contest on "the Nature of Time" (2008). v2: 2015 update, partially rewritten and extended for Foundations of Physics. arXiv admin note: substantial text overlap with arXiv:0810.061

Quantum decoherence of phonons in Bose–Einstein condensates

We apply modern techniques from quantum optics and quantum information science to Bose–Einstein condensates(BECs)in order to study, for the first time, the quantum decoherence of phonons of isolated BECs. In the last few years, major advances in the manipulation and control of phonons have highlighted their potential as carriers of quantum information in quantum technologies, particularly in quantum processing and quantum communication. Although most of these studies have focused on trapped ion and crystalline systems, another promising system that has remained relatively unexplored is BECs. The potential benefits in using this system have been emphasized recently with proposals of relativistic quantum devices that exploit quantum states of phonons in BECs to achieve, in principle, superior performance over standard non-relativistic devices. Quantum decoherence is often the limiting factor in the practical realization of quantum technologies, but here we show that quantum decoherence of phonons is not expected to heavily constrain the performance of these proposed relativistic quantum devices